Thermal printing devices of the general type with which the present invention is concerned are known. They operate with a supply of tape arranged to receive an image and means for transferring an image onto the tape. In one known device, a tape holding case holds a supply of image receiving tape and a supply of an image transfer ribbon, the image receiving tape and the transfer ribbon being passed in overlap through a printing zone of the printing device. At the print zone, a thermal print head cooperates with a platen to transfer an image from the transfer ribbon to the tape. A printing device operating with a tape holding case of this type is described for example in U.S. Pat. No. 4,815,871, (Varitronics, Inc.). Other printing devices have been made in which letters are transferred to an image receiving tape by a dry lettering or dry film impression process. In all of these printing devices, the construction of the image receiving tape is substantially the same. That is, it comprises an upper layer for receiving an image which is secured to a releaseable backing layer by a layer of adhesive.
Once an image or message has been printed on the tape, that portion of the tape is cut off to enable it to be used as a label. The releaseable backing layer is removed from the upper layer to enable the upper layer to be secured to a surface by means of the adhesive layer.
In another known printing device, described in U.S. Pat. No. 5,927,278, (Brother Kogyo K.K.), a tape holding case houses a supply of a transparent image receiving tape and a supply of an image transfer ribbon. The tape holding case also houses a supply of backing tape which comprises a carrier layer having an adhesive layer on its underside to which is secured a releaseable backing sheet and an adhesive layer on its upper side which can be secured to the image receiving tape after an image has been printed thereon. In this device, the image is printed onto the image receiving tape as a mirror image which, when viewed through the image receiving tape, is the correct way round. With this device, the print is protected when the label is used.
In all of these devices, the color of the label and the color of the print are predetermined by the contents of the tape holding case. By the color of the label reference is made to the upper layer of the image receiving tape of the apparatus described in EP-A-0267890 and to the carrier layer of the device described with reference to EP-0322918. The color of the print is determined by the color of the image transfer ribbon. Thus labels of one particular color can only be printed with ink of a particular color. Moreover, because the image receiving tape and image transfer tape are in the same tape holding case, they will run out together.
In another device disclosed in U.S. Pat. No. 4,480,936, two separate cassettes are provided which clip together to form a single unit which can then be inserted in a machine, the cassettes supplying ink ribbon and substrate tape from a side location towards a print station. In order to replace one cassette with another it is necessary to unclip the cassettes, replace the required cassette and reclip the new cassettes together before inserting them in a device. This makes the system awkward to use.
In another device, there are two cassettes with an ink ribbon cassette being located within a substrate tape cassette in a nested fashion, on a common side of the print zone. This means that it is fiddly and awkward to remove the ink ribbon cassette to change it. Also, the external dimensions of the ink ribbon cassette are determined by the dimensions of the substrate tape so that its size or capacity could only be increased at the expense of the substrate tape.
One printing device which overcomes the above problems is known from U.S. Pat. No. 5,458,423. That document discloses a printing device which has first and second cassette receiving portions arranged on opposed sides of a printing zone. The first cassette receiving portion is for receiving a tape holding case housing a supply of image transfer ribbon. The second cassette receiving portion is for receiving a tape holding case housing a supply of image receiving tape. In this way, the first and second tape holding cases can be individually removable and replaceable.
That printing device has a wide range of applications. However, it has the restriction that the widths of image receiving tape which are available currently have a maximum width of 19 mm. At present, tape widths of 6 mm, 12 mm and 19 mm of image receiving tape are available. These all cooperate with image transfer ribbon having a width of 19 mm. However, it is desirable to provide larger widths of image receiving tape, for example 24 mm and 32 mm. Clearly, image transfer ribbon having a width of 19 mm is not wide enough for the full extent of image receiving tape having a width of 24 mm or 32 mm. It would be desirable therefore to provide a tape holding case of image transfer ribbon having a greater width. This however presents a problem in the printing device of the type described in U.S. Pat. No. 5,458,423 that, if both widths of image transfer ribbon were available, a user could inadvertently attempt to use a tape holding case having an image receiving tape of a small width with a tape holding case having an image transfer ribbon of a large width (or vice versa). In the first case, the ink ribbon would extend beyond the image receiving tape and thus could transfer ink to the platen. In the second case, the image transfer ribbon would not be wide enough to transfer ink across the full extent of the image receiving tape.